Following this thread.
http://forum.arduino.cc/index.php?topic=397902.0
I am revisiting an old idea.
With mems technology now available i think it may be possible.
I am concentrating on the grid eye as a basis although others are available.
My proposal is to use a reflecting newtonian telescope and mount the detector at the focus.
Purpose is to detect people at a distance.
Two reasons, to extend the range of currently available occupancy sensors for safe and economic control of lighting, and security applications.
Reflector is 8 in with a focal length of 500 mm ( sorry about that ,sewing tape measure).
Detector has a lens with viewing angle of 60 degrees but i know no other details of the optics.
Reason for the reflector is to avoid the high cost of germanium lenses.
It will of course eventually use an arduino but for testing purposes i intend to use the digi key dev board with usb and development software.
So questions are.
1/How do i match the detector to the reflector, i may be able to stretch to a germanium singlet for this.
2/I purpose to cool the reflector, but how much will i need ?
I have boiling liquid nitrogen as an option which i would like to avoid.
I also have a closed loop refrigerator capable of -40 deg C for a smallish mass. (Pipe freezer).
3/ should i take a pill and go to bed ?
Interesting idea. Reflector as wideband device is a good idea. That's used in military grade IR imaging.
Have you tried this at room temperature? Us some IR source and measure response. Adjust the focus on your detector.
It will be interesting to measure the signal/noise ratio with cooler mirror.
What is the range you are hoping for for a Hot Human??
Agreed, this is an interesting idea!
If you are thinking of using the Melexis sensor(s), they effectively don't see highly polished metal surfaces because the emissivity is so low. I suspect that cooling the reflector is NOT necessary, so try it without cooling first.
You might also be able to get away with a much shorter focal length reflector, like a big flashlight reflector (torch reflector for you Brits 
).
Cooling IMO will be an issue only with very low signals in astronomy. For terrestrial applications the distinction between humans, cattle or hot motors may be required, at different sensitivity and image resolution.
In how far will your project perform better than IR cameras, like wildlife cameras or ordinary (webcam, smartphone...) cameras with IR filter removed?
like wildlife cameras or ordinary (webcam, smartphone...) cameras with IR filter removed?
Those detect a wavelength range of around 1 - 0.4 microns.
Humans (and other similarly warm objects) emit IR radiation peaking at about 9-10 microns. You need different detectors for that range.